1. Field of the Invention
The present invention relates to an image-scanning apparatus which has a shading correction function and a reference plate used for making a reference data for the shading correction.
2. Description of the Related Art
Image-scanning devices which have a CCD sensor for converting an optical image into an electrical signal are very popular. The electrical signals are subjected to a shading correction circuit before providing image data. The shading correction circuit corrects the scattering of the electrical signals. This type of image-scanning devices are, for example, disclosed in U.S. Pat. No. 5,206,501. This image-scanning device has a reference plate, and generates a reference data by using the reflected light quantity from the reference plate. The shading correction circuit performs a shading correction operation on the basis of the reference data. The image-scanning device radiates a light to the reference plate before an image-scanning operation, and makes the reference data.
Recently, as disclosed in, for example, U.S. Pat. No. 4,720,729, image-scanning devices which have a so-called zoom indicating function have been provided. This type image-scanning device indicates an image-reading area by a scale arranged on a carriage, and the carriage is positioned at a place under a platen before the scanning operation. This function is very helpful especially, for an operator who is not familiar with the image-scanning device, because the carriage indicates the position at which an original should be placed.
However, when both the shading correction function and the so-called zoom indicating function are adopted, the time period it takes to scan an original image is long because the carriage has to move from the position at which the carriage indicates an image-reading area, to the reference plate before starting the scanning operation.